This application is an improvement in die casting sand cores and core coatings disclosed in applicant's assignee's U.S. Pat. Nos. 4,413,666 issued Nov. 8, 1983 and No. 4,766,943 issued Aug. 30, 1988 to Enno H. Page and U.S. Pat. No. 4,529,028 issued July 16, 1989 to Dybala and Maczko.
There are many patents on processes for producing die castings and dies using expendable cores with various compositions of coatings for the dies and the cores therefor to withstand the hot metals poured or injected into the dies until the metal are solidified. Even applicant's assignee owns the above mentioned related patents and patent applications which disclose expendable sand cores having coatings, which cores have good shake-out properties, good wash-out resistance, good resistance to surface penetration, good shelf life, and high core strength to withstand pressures in excess of 1000 psi to from smooth undercut regions in die castings.
Nevertheless, still higher pressures in die casting processes are often desired and therefore it is essential to increase the strength of the expendable cores used therein. Applicant, after considerable experimenting and testing, has unexpectedly discovered new compositions and additives for the coatings of such expendable sand cores for die casting dies, which coated cores have improved physical properties over what has been known before; namely to withstand greater pressures and hotter metal melts, and to produce better and smoother undercut portions in die castings.